Context-Dependent Control of Erosion Resistance in Intertidal Flats: The Central Role of Bulk Density Across Natural and Restored Systems

Intertidal flats are highly dynamic coastal environments that provide vital ecosystem services. Despite their importance, intertidal flats are declining worldwide. In response, a range of restoration and management measures are increasingly being applied to enhance sediment accumulation and stabilize the bed surface. However, the effectiveness of these interventions ultimately depends on how sediment properties and bed stability develop over time. Quantitative understanding of these properties in natural and restored intertidal areas remains limited because field measurements are scarce, spatial heterogeneity is high, and hydrodynamic forcing is highly variable. Here, we quantify differences in key sediment properties between natural and restored intertidal flats to identify bed stability. We sampled sediments and measured key in situ bed characteristics at 16 intertidal sites in the Dutch Eastern and Western Scheldts, spanning multiple restoration strategies (i.e., managed realignments, groynes, and sediment nourishments) and natural locations. Our results show that restoration sites differ in sediment characteristics, with bulk density as the most consistent predictor of critical shear stress, an indicator of bed stability. These findings provide new insights into erosion thresholds in intertidal environments and can help inform adaptive coastal management of restoration measures under accelerating intertidal loss.